Osteoarthritis (OA), also commonly referred to as degenerative joint disease, is recognized in humans and all veterinary species (Richardson et al., (1997) Vet. Clin. North Am. 27:883-911). OA is a prevalent and debilitating disease in canines and is often associated with hip dysplasia (Martinez, S. (1997) Osteoarthritis, Vet. Clinics of N. Am.: Small Animal Practice 27 (4):735-758.). There is a high degree of similarity between canine and human osteoarthritis, thus making it an excellent animal model for the study of human osteoarthritis. While causative factors remain largely unknown, the disease is characterized by the imbalance of cartilage matrix degradation outweighing cartilage matrix synthesis. Chondrocyte apoptosis and inflammation may also be associated with the disease (Pelletier, J., et al. (2001) Arthritis & Rheumatism 44 (6):1237-1247; Lotz, M. (1999) Osteoarthritis and Cartilage 7: 389-391).
The disease is typically slow in progression and characterized by degeneration of articular cartilage with a loss of both proteoglycan and collagen and by proliferation of new bone. In addition, an inflammatory response can occur within the synovial membrane. Canine osteoarthritis can arise as a secondary condition resulting, in particular, from hip displasia or from osteochondritis dissecans (Martinez, supra). Acquired conditions involving traumatic events can also lead to osteoarthritis in the dog (Martinez et al., Vet. Clin. North Am. 27:759-775, 1997). Treatment modalities for osteoarthritis can include the administration of anti-inflammatory drugs as well as the manipulation of dietary fatty acids (Richardson et al., supra).
Diagnosis of canine osteoarthritis is typically based upon symptomotology. Dogs having osteoarthritis show a lameness which may have a gradual onset but can flare up acutely after exercise. The lameness is exacerbated by rest but decreases after a few minutes of activity. Cold damp conditions, obesity and prolonged exercise often worsen signs of lameness (Pederson et al, in Textbook of Veterinary Internal Medicine, 5th Ed., Ettinger et al., ed., W.B. Saunders and Co., Philadelphia, 2000, pp. 1862-1886).
With the emergence of the genomic sciences, it has become apparent that not only is the regulation of gene expression intimately involved in normal homeostasis, alterations in the differential expression of genes is one aspect in the development of diseases. As a result, the evaluation of gene expression patterns in disease has become increasingly recognized as being crucial to the understanding of disease processes at the molecular level. (Going et al., European J. Cancer 35:1895-1904, 1999; Wang et al., Cardiovasc. Res. 35:414-421). A number of approaches have emerged for studying comparative gene expression and the current emphasis has been on high throughput analysis methods. (for review see Carulli et al, J. Cell. Biochem. Suppl. 30/32:286-296, 1998; Kozian et al., Trends Biotechnol 17:73-78, 1999). Recent methods developed for high throughput analysis of differential gene expression include, for example, EST sequencing (Adams et al., Science 252:1651-1656, 1991; Adams et al., Nature 377:3-16, 1995), microarray hybridization (Schena et al., Science 270:467-470, 1995), and differential display (Liang et al., Science 257:967-970, 1992; Welsh et al., Nucleic Acids Res. 20:4965-4970, 1992).
Gene expression in osteoarthritis, and particularly in canine osteoarthritis, has not been comprehensively studied. Accordingly, a need exists to identify nucleic acid sequences and their encoded proteins which are differentially expressed in osteoarthritis. This information would be useful to diagnose the osteoarthritic disease state, or pre-disposition to the disease, in a subject, as well as to identify substances useful in the treatment or prevention of osteoarthritis.